What can Gaia (with TMT) say about Sculptor's Core?

TL;DR

This paper explores how Gaia and the upcoming TMT can measure stellar motions in Sculptor to constrain its dark matter profile, potentially distinguishing between cored and cuspy models with high confidence.

Contribution

It demonstrates that combined Gaia and TMT observations can significantly improve constraints on Sculptor's dark matter density profile and core/cusp nature.

Findings

Gaia can measure proper motions of 139 stars with 13-20 km/s precision.

Combined Gaia and TMT data can determine the dark matter density slope gamma with high accuracy.

Results suggest Gaia and TMT can exclude cored profiles predicted by CDM with high confidence.

Abstract

Walker et al.'s Magellan/MMFS Survey survey identified 1355 red giant candidates in the dwarf spheroidal galaxy Sculptor. We find that the Gaia satellite will be able to measure the proper motions of 139 of these with a precision of between 13 and 20 km/s. Using a Jeans analysis and 5-parameter density model we show that this allows a determination of the mass within the deprojected half-light radius to within 16% and a measurement of the dark matter density exponent gamma to within 0.68 within that radius. If, even at first light, the TMT observes Sculptor then the combined observations will improve the precision on these proper motions to about 5 km/s, about 5 years earlier than would be possible without Gaia, further improving the precision of gamma to 0.27. Using a bimodal stellar population model for Sculptor the precision of gamma improves by about 30%. This suggests that Gaia (with TMT) is capable of excluding a cored profile of the kind predicted by CDM simulations with 2 sigma (4 sigma) of confidence.